Propeller blade construction



Sept. 22, 1953 F. M. LE COMPTE PROPELLER BLADE CONSTRUCTION Filed March 31 1950 2 Sheets-Sheet l INVENTOR. FRflA/K M. M COMP/2 S p 1953 F. M. LE COMPTE ,65 ,897

I PROPELLER BLADE; CONSTRUCTION Filed March 31 1950 2 Sheets-Sheet 2 INVENTOR.

F/EHNK M LE LOMPTE BY Patented Sept. 22, I953 2,652,897 PROPELLER BLADE CONSTRUCTION Frank M. Le Compte, Chatham, N. J assignor to Curtiss-Wright Corporation, a corporation of Delaware Application March 31, 1950, Serial N 0. 153,255 2 Claims. Cl. 170159) This invention relates to propeller blades for aircraft and to the manufacture thereof.

Hollow metallic propeller blades are well known in the art, and many techniques have been proposed and used in the manufacture of such blades. Manufacture of hollow steel blades presents a number of different and difficult fabricating problems which result from requirements of high precision in manufacture, and the perfection of manufacturing technique which is required to endow the blades With adequate strength concurrently with minimum weight. The thin leading and trailing edges of hollow steel blades have always presented a rather serious problem due to the high vibratory stresses which occur in the propeller blades, these edge portions of the blades being likely to develop cracks if the steel of which the blade is made, and any materials added thereto, are not of the highest quality and free from defects. A further requirement in propeller blades generally is resistance to abrasion and this resistance particularly at the leading edge of the blade is best met by using relatively hard steel materials.

The present invention proposes to fabricate a hollow steel propeller blade from a seamless steel tube and to so form the tube that the airfoil portion of the propeller blade will comprise separate steel camber and thrust plates joined at their edges by a strong rubber bond. The rubber provides high resistance to fatigue and if appropriately applied provides adequate strength in the propeller blade to make it an adequate structure to resist the various loads and vibrative stresses to which the blade is subject in opera-. tion. As one of the features of the invention,'

the rubber bond between the blade plates is so located that it will not interfere with the leading or trailing steel edges of the blade so that the latter can be depended upon to yield high abrasion resistance.

Objects of the invention will become apparent from the above brief description and from the following detailed description when taken in connection with the drawings in which similar reference characters represent similar parts and in which Fig. l is a plan view of a typical propeller blade according to the invention;

Fig. 2 is a perspective elevation looking toward the tip end of the propeller blade;

Fig. 3 is an enlarged typical cross-section of the blade taken on the line 3-3 of Fig. 1;

Fig. 4. is an end elevation of a typical form of seamless tube from which the propeller blade is fabricated;

Fig. 5 is an enlarged section through a portion of the tube showing a first stage in the manufacture of the blade;

Figs. 6, '7 and 8 are fragmentary sections of portions of the blade tube showing consecutive steps in the fabrication of a propeller blade; and

Fig. 9 is a cross-sectional view of a blade airfoil section showing an alternative structural arrangement of the parts thereof.

Fig. 1 designates generally a typical blade whose planiform is adapted for the manufacturing techniques of the invention. In this arrangement, l0 shows a cylindrical butt adapted for securement in a propeller hub, the butt including a flange l l to enable retention of the blade in the hub. A so-called cuff ring is shown at l2 which is usually provided in the blade butt to enable thickening or upsetting of the butt end and further to provide means for securing a cuff on the propeller blade if such is desired.

The butt blends into a blade shank portion I 4 tapered in planiform and reversely tapered in edgewise form, blending the butt into the airfoil portion l5 of the propeller blade. The leading and trailing edges l6 and I! respectively of the airfoil l5 are substantially straight and parallel and terminate at a blade tip portion l8 which may be flat as shown, or curved outwardly according to the desire of the blade designer.

According to this invention, the blade airfoil portion l5 comprises a camber plate 2!] and a thrust plate 2|, the two plates being joined together at the leading edge by a rubber filleting mass 22 and at the trailing edge by a rubber filleting mass 24, said masses 22 and 24 being exposed in part to the camber surface of the blade as at 26 and 28 whereat they form a portion of the airfoil section of the propeller blade, and isolate the thrust and camber plates from one another. The rubber provides a vibration absorber if there is relative vibration between the thrust and camber plates, and due to the high fatigue resistance of the rubber, possible plate failures adjacent the leading and trailing edges are prevented. If desired, a central rubber rib 30 may also be applied within the blade, joining the thrust and camber plates, or in very thin blades, it may be desirable to have the rubber solid throughout the interior of the blade airfoil section or part thereof.

According to this invention, the thrust plate of the blade forms the principal structural member and carries a thickened leading edge portion 32 and a thickened trailing edge portion 34 integral therewith, said leading and trailing edge portions being of parent material with the thrust "blade are trimmed off as shown in Fig.

plate 2i and thus having high resistance to abrasion. These edges likewise stiffen the propeller blade giving it adequate torsional and bending rigidity.

A preferred mode of fabricating a blade of the type described will be given. A seamless steel tube such as 38 in Fig. 4 is machined or otherwise formed to provide thickened portions .38'and M3 on the exterior of the tube, the upper margins of these thickened portions terminating substantially on a diameter of the tube as noted. The shank and butt portions of the ultimate propeller blade may be formed in any desired manner from the tube itself, by extrusion techniques utilized in forming the tube, or by the attachment o'f-a separate preformed member to the basic tube.

After formation of the tubearrangement shown in Fig. 4, the tube is placed in a forming press and flattened to the form shown in Figidwherein the thickened portions 38 and 40 are transferred to the inside of the tube and wherein the thin upper portion of the tube of Fig. iis flattened to fold sharply over the thickened portions 38 and id, leaving the folded edges 42 and 44. In flattening the tube, it is preferable to do so in forming dies so that the rudimentary camber plate 26] and the rudimentary thrust plate 2| are given'approximately the configuration which they will have in the ultimate propeller blade. After flattening, operations indicated in Fig. 6 are performed which include first, slitting the edges of the camber member 2i) as at lfi, longitudinally, whereby the cambermember is parted from the thrust member 2! throughout substantially the entire airfoil section of the propeller blade. Reference may briefiy be made to Fig. l in which these slits are indicated at 46, later filled with rubber to provide the surfaces 26 and extending from the blade tip inwardly to the transition zone between the shank l4 and the lacle airfoil sectionlti. Afterslittingas at 46, the foldededges M and 42 of the rudimentary 6 along the line such as'd8, whereupon a camber plate portion St between the folded portion '44 and the slit '56 'is lifted away. The .rudimentary blade now comprises the'butt-Iil, the shankl4 and two unattached rudimentary camberand thrust elements 2i! and 2 l, the edges of which are in spaced relation as at 52.

Afterthe slitting and trimming operations, the thickened portions 32 and of the thrust plate are trimmed to the form shown in Fig. 7 whereby they conform to the desired edge profile of the ultimate propeller blade. Thereupon, therudimentary propeller blade is placed between formed dies having recesses complementary to the desired final airfoil section "of the propeller blade. Suitable mandrels are placed'between the thrustand camber plates 22 and 2| in 'a manner such as that described and indicated in my copending patent application Serial'No. 55,264,filed October 19, 1948 now Patent No. 2,581,193. Thereupon, rubber is injected under pressure into the leading and trailing edge cavities of the propeller blade and bonded to the elements thereof, resulting in an edge configuration as shown in Fig, 8 and also in Fig. 3. If desired, as heretofore noted, a central rubber rib (Fig. 3) maybe injected at the same time as the rubber edge fillets 24 and 22 are injected, or the blade may be wholly filled if the design calls for such filling. The techniques for rubber injection and bonding described in said copending application may be used in the fabrication of the propeller blade herein disis reduced. For

cause of the lesser thickness is :a solid substance having .ance, and elasticity which is great compared to 4 closed, or any other appropriate techniques may be utilized.

After formation of the rubber bonding fillets within the airfoil portion of the propeller blade, the blade is removed from the forming dies and the mandrels are removed from within the propeller blade whereupon the blade is completed except for final polish and finishing operations and such other operations as may be required in the machining of the butt l0 and in balancing the blade. Preferably, the tip l8 of the propeller blade is provided with a rubber fillet 56 shown in Fig. 1, joining the thrust and camber plates 20and 2| 'atthe same time as rubber is injected to form the fillets 22 and 24 and the rib 30 if the latter is required.

In Fig.9 an alternative arrangement is shown wherein the edges of the camber plate 20 are offset toward the thrust plate 2| so that the distance between the edges of the respective plates this arrangement, these offsets being shown at wand 60, bonding area between the thrust and camber plates may be increased and the rigidity may likewise be increased beof filleting, rubber between the plates. If this offset arrangement is used, the rubber of the fillets 24 and 22 will extend over the exterior of the edges of the camber plate 20 as at 62 and 64 to provide a smooth continuation of the airfoil cross-section of the propeller blade.

The blade herein described and shown may incorporate other well known provisions for reinforcing and stiffening and alternative metallic ribs are disclosed in the drawings in dotted lines in Fig. 9. They may be incorporated in the propeller for stiffness and strength in a manner well known in the art.

'Where the term rubber is used hereinit is intended .to comprehend natural, artificial, or syntheticmubber-like materials and also, various yieldable plastic materials akin to rubberin their physical qualities. Essentially, the rubber-like material appropriate 'for use in this invention high fatigueresistthat of the parent metal, such as steel, used for the thrustand camber bladeplates and for the other structural components of the propeller blade.

It will'be noted in the blade of this invention that the principal centrifugal loading thereon is carried by parent steel material all the way from the blade tip to the blade butt.

Though but a single embodiment illustrating the invention has been illustrated and described, it is to be understood that the invention may be applied in various forms. Changes may be made in the arrangements shown without departing from the spirit or scope of the invention as will be apparent to those skilled in the art-and reference should be made to the appended claims for -a definition of the limits of the invention.

What is claimed is: 1. An aircraft propeller blade comprising a hollow shank portion and bifurcated flattened blade portions extending therefrom including a thrust member and a camber member, said thrust member having thickened leading and trailing edge portions defining the leading edge and trailing eds of the blade,.and said camber member lyinc spaced from and within the margins of said thrust member, the camber member edges lying inboard of said thickened edge portions of the thrust member, masses of rubber along and within the leading and trailing edges of said blade,

said masses being bonded to said members at their inner faces, a portion of each rubber mass forming an exposed part of the blade camber surface between the edge of said camber member and the thickened portion of said thrust member inboard of the edge of the thrust member.

2. A hollow metal propeller blade assembly having at one end a hollow tapered shank portion and at the other end a bifurcated flattened, edge-separated thrust and camber members bonded to one another adjacent the leading and trailing blade edges by rubber forming a blade portion, one of said members extending chordwise beyond the bonding rubber to provide metallic leading and trailing blade portion edges, said blade having a typical cross-section wherein the thrust member is thickened along each edge, the camber member is narrower than and spaced apart from said thrust member forming gaps between said members inwardly of the leading edge and trailing edge, and wherein the bonding rubber fills said gap and forms part of the eX- ternal airfoil profile of the blade portion, said rubber extending inwardly in a chordwise direction, between the members and being bonded thereto to provide the sole lateral edge joints therebetween in the flattened blade portion of the assembly.

FRANK M. LE COMPTE.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,106,761 Roberts Feb. 1, 1938 2,280,337 McKee Apr, 21, 1942 2,323,165 Thomas June 29, 1943 2,400,649 Larsen May 21, 1946 2,442,641 Duncan June 1, 1948 2,457,202 Brady Dec. 28, 1948 2,465,007 Bragdon Mar. 22, 1949 2,506,992 Bucher May 9, 1950 2,544,450 Enos Mar. 6, 1951 FOREIGN PATENTS Number Country Date 439,407 Great Britain Dec. 5, 1935 958,272 France Sept. 12, 1949 

